This invention relates to flexographic printing, and more particularly to tapes or carriers for flexographic printing that allow egress of trapped air.
Flexographic and/or letterpress printing is a printing processes utilizing flexible printing plates with relief printing surfaces. The basic flexographic process consists of a flexible and at least minimally compressible planar printing plate bearing a relief image of the information to be printed. The printing plate may be adhesively attached to a carrier in a printing machine to form a flexographic printing system. The carrier may be a drum-like structure, a cylindrical sleeve, or a continuous belt. The carrier is precisely machined to an appropriate diameter to allow printing at necessary repeat lengths. The carrier and attached printing plates may be inserted into the print machine to conduct the printing process.
In the flexographic printing process the printing plate moves past an inking station, where a layer of ink is applied onto the relief image surface of the plate. Next, the carrier moves the ink carrying relief image to the transfer station, where the ink layer is contacted with a receptor substrate surface. When the printing plate separates from the substrate, the ink film splits, which leaves a printed image of the relief pattern on the substrate. Each ink transfer normally occurs in a nip or planar mode using precisely controlled pressure on the printing plate. This controlled pressure maintains print quality by controlling the thickness and uniformity of the ink film applied on the surface of the receptor substrate. Additional carrier layers, cushion layers and tie layers may be included in the flexographic printing element.
Typically, a double-coated tape construction is used to mount the printing plate on the carrier. First, the tape is unwound from a roll, a layer of adhesive is exposed, and the adhesive layer is adhered to the carrier. Next, the release liner is removed from the opposite side of the tape and the flexographic printing plate is attached thereto. To maintain print quality, the printing plate should be carefully attached to the carrier, and often the first attachment is not successful. For example, it may become necessary to reposition the plate to maintain precise registration with the carrier. During attachment and any necessary repositioning, air is often trapped at interfaces between the printing plate and the tape, or between the tape and the carrier. Fugitive air bubbles cause pressure variations between the printing plate and the carrier, and represent one of the leading causes of print defects in flexographic printing processes. Typically, flexographic printers remove trapped air with syringes and razor knives after the printing element is in the press, which damages the printing plates and results in increased prepress costs and excessive pressroom downtime. Air bubbles have a significant impact on flexographic print quality at high resolution, which negatively impacts the future of flexographic printing as a viable alternative to offset and gravure printing.
To reduce air entrapment, adhesives may be applied in distinct patterns to the opposed surfaces of the tapes. For example, adhesive may be applied in a striped or corrugated pattern that includes alternating strips of coated areas and non-coated areas. While effective at bleeding air, these tapes typically do not have sufficiently reliable adhesion to maintain precise carrier/plate registration at high print rates. Irregular patterns of bumps and pebbles, or hills and valleys, such as those used in crepe-like tapes, are also capable of bleeding a limited amount of air, but the irregular nature of the pattern causes air entrapment under portions of the tape surface, as well as inconsistent levels of adhesion. These tapes are also difficult to reposition on the carrier.
Japanese patent application HEI 8-100155 describes a double-coated adhesive tape that may be applied to a printing plate in a flexographic printing process. In the tape construction described in the JP ""155 application a backing is through embossed to form an uneven surface on both sides. A pressure sensitive adhesive is then solvent coated on each of the opposed surfaces of the embossed backing to form a double-coated tape capable of releasing entrapped air. However, since the patterns on the opposed surfaces are the reverse images of each other, the air bleed and adhesion at each surface are difficult to precisely control independently of the shape of the backing. In addition, if the embossed adhesive element is used to attach a printing plate to a carrier, the embossed pattern may carry through to the printed surface. This problem becomes increasingly acute in high-resolution flexographic printing processes.
While many adhesive constructions and materials are known, no conventional adhesive materials are available that have properties suitable for flexographic printing applications.
In a first embodiment, the invention is a carrier for a flexographic printing plate. The carrier includes a surface and a tape on the surface. The tape includes a first adhesive layer on the surface, a substrate on the first adhesive layer, and a second adhesive layer on an opposite side of the substrate, wherein the substrate is substantially smooth. At least one of the first and second adhesive layers is preferably substantially continuous and comprises a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm.
In a second embodiment, the invention is a method for mounting a printing plate. The method includes providing a carrier for a flexographic printing plate, wherein the carrier has a mounting surface. A tape is provided that includes a first adhesive layer, a substrate on the first adhesive layer, and a second adhesive layer on an opposite side of the substrate, wherein the substrate is substantially smooth. At least one of the first and second adhesive layers is preferably substantially continuous and comprises a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm. The first adhesive layer is then applied to the mounting surface of the carrier. A printing plate may then be applied to the second adhesive layer of the tape.
In a third embodiment, the invention is an adhesive tape for flexographic printing that includes a first adhesive layer, a substrate on the first adhesive layer, and a second adhesive layer on an opposite side of the substrate. The substrate may include a foam layer, at least one substantially smooth polymeric film layer, or combinations thereof. At least one of the first and second adhesive layers is preferably substantially continuous and has a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm.
In a fourth embodiment, the invention is a method for flexographic printing that includes providing a carrier for a flexographic printing plate, wherein the carrier has a mounting surface. A tape is then provided that includes a first adhesive layer, a substrate on the first adhesive layer, and a second adhesive layer on an opposite side of the substrate, wherein the substrate is substantially smooth. At least one of the first and second adhesive layers is preferably substantially continuous and comprises a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm. The first adhesive layer of the tape is applied to the mounting surface of the carrier, and a printing plate is applied to the second adhesive layer of the tape. Ink is applied on the printing plate, and then the ink is applied to a substrate.
In a fifth embodiment, the invention is a printing device including a carrier for a flexographic printing plate. The carrier includes a surface and a tape on the surface. The tape includes a first adhesive layer on the surface, a substrate on the first adhesive layer, and a second adhesive layer on an opposite side of the substrate, wherein the substrate is substantially smooth. At least one of the first and second adhesive layers is preferably substantially continuous and comprises a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm. A printing plate is adhered to the second adhesive layer of the tape.
In a sixth embodiment, the invention is a printing plate for flexographic printing, including a printing plate with a lower surface and a relief surface. A mounting tape is on the lower surface of the printing plate, wherein the mounting tape includes a substantially smooth substrate with a first surface attached to the lower surface of the printing plate and an adhesive layer attached to a second surface of the substrate opposite the first surface. The adhesive layer is preferably substantially continuous and includes a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm.
In a seventh embodiment, the invention is a printing plate for flexographic printing. The printing plate has a lower surface and a relief surface. An adhesive layer is on the lower surface of the printing plate. The adhesive layer is preferably substantially continuous and includes a regular pattern of permanent grooves. The grooves preferably have a depth of about 4 xcexcm to about 200 xcexcm, and a width of about 4 xcexcm to about 200 xcexcm.
In an eighth embodiment, the invention is a printing plate for flexographic printing, wherein the plate has a relief surface and a lower surface opposite the relief surface, and wherein the lower surface includes a pattern of grooves.
In a ninth embodiment, the invention is a carrier for a printing plate in a flexographic printing press, wherein the carrier has a mounting surface for the printing plate, and wherein the mounting surface includes a pattern of grooves.
The flexographic printing tapes of the invention include adhesive layers with sufficient surface contact to effectively adhere to the printing plate carrier at high print rates. The grooves in the tape of the invention allow egress of air trapped during application of the tape to the carrier, or during application of the printing plate to the tape. This allows more precise carrier/plate registration, which improves print quality and reduces the time required to change printing plates. The flexographic printing tapes of the invention reduce the damage and excessive wear to expensive printing plates caused by trapped air bubbles, which reduces printing costs. In addition, the dimensions and design of the grooves in the tapes of the invention limit the rate of ingress of fluids, for example, cleaning solutions, compared to strip coated tapes or tapes with larger features.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.